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We are publishing a transcript of a lecture by Aleksey Bobrovsky, Senior Researcher at the Department of Macromolecular Compounds, Faculty of Chemistry, Moscow State University, Associate Professor, Doctor of Chemistry, laureate of the Presidential Prize for Young Scientists for 2009, delivered on December 2, 2010 at the Polytechnic Museum as part of the Polit. RU".

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Lecture text. Part 1

Good evening! I would like to slightly change the regulations: the lecture consists of two parts: first, liquid crystals, then liquid crystal polymers, so I would like to suggest asking some questions after the first part. It will be easier.

I would like to say that the main task that I set for myself when preparing for this lecture is not so much to load you with an abundance of information about liquid crystals, about their use, but to somehow interest liquid crystals, to give some initial concepts: what they are and show how beautiful and interesting they are not from a utilitarian point of view (where they can be used), but from the point of view of science and art (how beautiful they are in themselves). Plan of my report.

First of all, I will tell you when and how the liquid crystal state was discovered, what is the uniqueness of liquid crystals in comparison with other objects, and in the second part of my report I will talk about liquid crystal polymers and why they are interesting and remarkable.

Everyone is well aware that in most substances the molecules form a crystalline state, the molecules form a three-dimensional crystal lattice ordered in three dimensions, and when heated to a certain temperature, a phase transition is observed from a three-dimensional ordered state to a disordered liquid state, and upon further heating - to a gaseous state . It turned out that there are some intermediate phases that have the state of aggregation of a liquid, but, nevertheless, have some order: not three-dimensional, but two-dimensional or some other degenerate order. I will now explain what is at stake.

The first report about an unusual state of matter - about the liquid-crystalline state of matter, then, however, this term did not exist - took place in 1888. According to some other sources, such an unusual state of the substance was also recorded in 1850, but it is generally accepted that in 1888 Friedrich Reinitzer, an Austrian scientist, studied the substance cholesteryl benzoate - a derivative of cholesterol - and found that when heated to 145 °, the crystalline phase (white powder) passes into a strange turbid liquid, and with further heating to 179 °, a transition into an ordinary transparent liquid is observed. He tried to purify this substance, as he was not sure that he had pure cholesteryl benzoate, but nevertheless these two phase transitions were reproduced. He sent a sample of this substance to his friend physicist Otto von Lehmann. Lehman was engaged in the study of ordinary crystals, including plastic crystals, which are soft to the touch, they are different from ordinary hard crystals. The main method of study was polarizing optical microscopy - this is a microscope in which light passes through a polarizer, passes through a substance, and then through an analyzer - through a thin layer of substance. When placed between a polarizer and an analyzer of crystals of a certain substance, one can see textures - characteristic pictures for different crystalline substances - and thus study the optical properties of crystals. It so happened that Otto von Lehmann was helped to understand what is the cause of the intermediate state, delusion. Otto von Lehmann was seriously convinced that all the properties of crystalline substances, crystals depend solely on the shape of the molecules, that is, it does not matter how they are located in this crystal, the shape of the molecules is important. And in the case of liquid crystals, he turned out to be right - the shape of the molecules determines the ability to form a liquid crystal phase (mainly the shape of the molecules). Here I would like to talk about the main historical stages in the study of liquid crystals, the most important in my opinion.

In 1888, Reinitzer wrote that there are crystals whose softness is such that they can be called liquid, then Lehman wrote an article on fluid crystals, in fact he coined the term liquid crystals. An important historical episode: in the 20-30s, the Soviet physicist Frederiks studied the influence of various magnetic and electric fields on the optical properties of liquid crystals, and he discovered an important thing that the orientation of molecules in liquid crystals changes very easily under the action of external fields, and these fields very weak and the changes are very fast. Since the end of the 60s, a boom in the study of liquid crystal systems, liquid crystal phases began, and it is associated with the fact that they learned how to use them. Initially, for information display systems in conventional electronic digital watches, then in calculators, and with the advent of computer technology, it became clear that liquid crystals can be actively used to make displays. Naturally, such a technological leap stimulated the study of liquid crystals from the point of view of fundamental science, but I would like to note what a big time gap there is between scientific discoveries related to liquid crystals. In fact, people were interested in them out of curiosity, there was no utilitarian interest, no one knew how to use them, and, moreover, in those years (20-30s) the theory of relativity was much more interesting. By the way, Fredericks is a popularizer of the theory of relativity in the Soviet Union, then he was repressed and died in the camps. In fact, 80 years have passed since the discovery of liquid crystals, until they learned how to use them. I often cite this example when talking about the specifics of science funding.

I would like to dwell on the main types of liquid crystal phase. How the mesophase, namely the liquid crystal phase, is arranged.

Typically, the liquid-crystal phase is formed by molecules having a rod-like or disk-like shape, that is, they have an anisometry of the form, first of all, rods or disks. One can imagine a good experiment that is easy to set up: if you randomly pour sticks into a box and shake it, then as a result of this shaking you will notice that the sticks themselves fit in parallel, and this is how the simplest nematic phase is arranged. There is an orientational order along some direction, and the center of mass of the molecules is disordered. There are much more complex phases, for example, of the smectic type, when the center of mass is in planes, that is, such layered phases. The cholesteric phase is very interesting: its local order is the same as that of the nematic phase, it has an orientational order, but at a distance of hundreds of nanometers a helical structure with a certain twist direction is formed, and the appearance of this phase is due to the fact that the molecules are chiral, that is, it is necessary to conduct molecular chirality (I will explain what it is later) to form such a helical twist. This phase has the same interesting properties as the nematic phase, and it can also find some application. The phases I talked about are the simplest. There are so-called blue phases.

I will dwell on them a bit when I talk about polymers, this is a bit related to my work. Here, these lines indicate the direction of orientation of the molecules, and the main structural element of such phases is such cylinders in which the orientation of the long axes of the molecules cleverly changes, that is, in the center of this cylinder, the orientation is along the axis of the cylinder, and as it moves away to the periphery, a turn is observed. These phases are very interesting from the point of view of structure, they are very beautiful in a polarizing microscope, and it is important to note that in the case of low molecular weight liquid crystals these phases exist in some tenths of a degree, at best 2-3 ° temperature interval, and in the case of polymers managed to fix these interesting structures, and I will talk about it later. A little chemistry. What do the structures of liquid crystal molecules look like?

Usually there is an aromatic fragment of 2-3 benzene rings, sometimes it can be two aromatic rings connected directly, there may be a linking fragment. It is important that this fragment is elongated, that is, its length is greater than its width, and that it is sufficiently rigid, and rotation around the long axis is possible, but during this rotation, the shape remains elongated. This is very important for the liquid crystal phase to form. The presence of flexible tails in the molecule is important - these are various alkyl tails, the presence of various polar substituents is important. This is important for applications, and it creates dipole moments and the ability to reorient in external fields, that is, this molecule is composed of two main parts: a mesogenic fragment with some kind of substituent (polar or non-polar) and a flexible tail that can bend. Why is it needed? It acts as an internal plasticizer, because if you take rigid molecules, they will crystallize - they will form a three-dimensional crystal without any mesophases, without liquid crystal phases, and a flexible tail often helps to form an intermediate phase between a crystal and an ordinary isotropic liquid. Another type of molecules are disk-shaped molecules. Here is the general structure of such disks, which can also form mesaphases, but they have a completely different structure than phases based on elongated molecules. I would like to draw your attention to how beautiful liquid crystals are in a polarizing microscope.

Polarizing microscopy is the first method for studying liquid crystals, that is, already from the picture that a researcher observes in a polarizing microscope of crossed polarizers, one can judge what kind of mesophase, what type of liquid crystal phase is formed. This is the typical picture for a nematic phase whose molecules form only an orientational order. This is what the smectic phase looks like. So that you can imagine the scale of all this, that is, it is much larger than the molecular scale: the width of the picture is hundreds of microns, that is, it is a macroscopic picture, much larger than the wavelength of visible light. And by analyzing such pictures, one can judge what kind of structure there is. Naturally, there are more accurate methods for determining the structure and some structural features of these mesophases - such methods as X-ray diffraction analysis, various types of spectroscopy - this allows us to understand how and why molecules are packed in one way or another.

Another type of picture is a concentrated solution of short DNA fragments (aqueous solution) - at the University of Colorado they got such a picture. Generally speaking, the importance and features of the formation of liquid crystalline phases in biological objects is a topic for a separate big discussion, and I am not an expert in this, but I can say that many polymers of a biological nature can give a liquid crystalline phase, but this is usually a lyotropic liquid crystalline phase, that is the presence of a solvent, such as water, is important in order for this liquid crystal phase to form. These are the pictures I received.

This is what cholesteric mesophase looks like - one of the typical pictures. I would like to show how beautiful phase transitions look: when the temperature changes, we can observe the phase transition.

When the temperature changes, a change in refraction is observed, so the colors change, we approach the transition - and a transition to an isotropic melt is observed, that is, everything darkens, a dark picture is visible in the crossed polarizers.

In the other case, it is a bit more complicated: at first, a dark picture is visible, but this nature deceives us, it’s just that the molecules are oriented so that they look like an isotropic melt, but there was a liquid crystal phase. Here is the transition to another liquid crystal phase - upon cooling, more ordered changes in orientation. The red color is associated with a helical structure with a certain helix pitch, and the helix pitch changes, the helix twists, so a change in colors is observed. Various disclinations are visible, that is, the spiral is twisted, and now at some point crystallization of this sample will be observed, all this will turn blue. I show this to the fact that one of my personal motives to deal with, for example, liquid crystals is their beauty, I look at them with pleasure through a microscope, I have the happiness to do this every day, and aesthetic interest is supported by scientific interest. Now there will be crystallization, everything takes place in real time. I don't have any bells and whistles, it's an ordinary soap dish mounted on a microscope, so the quality is appropriate. Here grow spherulites of this compound. This compound was synthesized for us by chemists in the Czech Republic. (We also synthesize LC compounds ourselves.) Little needs to be said about why they are widely used.

Each of us carries a small amount of liquid crystals with us, because all mobile phone monitors are liquid crystals, not to mention computer monitors, displays, television monitors, and serious competition from plasma monitors and LED monitors in general - as far as I know (I'm not an expert in this), no. Liquid crystals are stable, it doesn't take a lot of voltage to switch the picture - this is very important. An important combination is observed in liquid crystals, the so-called anisotropy of properties, that is, the unequal properties in different directions in the medium, their low viscosity, in other words, fluidity, it is possible to create some kind of optical device that would switch, react with a characteristic switching time milliseconds or even microseconds - this is when the eye does not notice the speed of this change, which is why the existence of LCDs and television displays is possible, and very high sensitivity to external fields. These effects were discovered even before Fredericksz, but investigated by him, and the orientational transition, which I will talk about now, is called the Fredericksz transition. How does a simple dial of an electronic watch work, and why are liquid crystals so widely used?

The device looks like this: there is a layer of liquid crystal; the sticks represent the direction of orientation in the liquid crystal molecule, of course they are not to scale, they are much smaller than the rest of the design, there are two polarizers, they are crossed so that if there were no liquid crystal layer, the light would not pass through them. There are glass substrates on which a thin conductive layer is applied so that an electric field can be applied; there is also such a tricky layer that orients the liquid crystal molecules in a certain way, and the orientation is set in such a way that on the upper substrate the molecules are oriented in one direction, and on the other substrate - in a perpendicular one, that is, a twist orientation of the liquid crystal molecules is organized, so the light , when it falls on the polarizer, it polarizes - it enters the liquid crystal medium, and the plane of its polarization rotates following the orientation of the liquid crystal molecule - these are the properties of liquid crystal molecules. And, accordingly, due to the fact that it rotates in plane polarization by 90 °, light in such a geometry passes quietly, and if an electric field is applied, the molecules line up along the electric field, and therefore polarized light does not change its polarization and cannot pass through another polarizer. This results in a dark image. In reality, a mirror on a wristwatch is used and segments can be made that allow you to visualize some kind of image. This is the simplest circuit, of course, liquid crystal monitors are much more complex structures, multilayer, the layers are usually very thin - from tens of nanometers to microns - but the principle is basically the same, and this transition, when the orientation of molecules changes along an electric or magnetic field ( monitors use an electric field because it is simpler), is called the Freedericksz transition (effect) and is actively used in all such devices. The first prototype is a nematic display in a dial.

And this is a picture illustrating how small an electric field it takes to reorient a liquid crystal molecule. In fact, this is a galvanic cell made up of two potatoes as an electrolyte, that is, a very small voltage in the region of 1V is needed for such a reorientation, which is why these substances have received such widespread use. Another application, and we are talking about cholesteric liquid crystals, which I will talk about in more detail, is due to the fact that they are able to change color depending on temperature.

This is due to the different pitch of the spiral, and it is possible to visualize, for example, the temperature distribution. I have finished with low molecular weight liquid crystals and am ready to listen to your questions on them before moving on to polymer liquid crystals.

Lecture discussion. Part 1

Tatyana Sukhanova, Institute of Bioorganic Chemistry: Answer the question of an amateur: in what range does the color of liquid crystals change, and how does this depend on their structure?

Alexey Bobrovsky: We are talking about cholesteric liquid crystals. Here the color changes depending on the pitch of the cholesteric helix. There are cholesterics that selectively reflect light in the UV region, respectively, the invisible region, and there are cholesterics that selectively reflect light due to this periodicity in the infrared region, that is, we are talking about microns, tens of microns, and in the case of color pictures, which I showed in polarizing optical microscopy, it is more difficult there, and the color is due to the fact that polarized light, the plane of polarization in a liquid crystal rotates differently, and this depends on the wavelength. There is a complex color gamut, and the entire visible range is closed, that is, you can contrive to get a variety of colors.

Boris Dolgin: Can you tell me a little more about life?

Alexey Bobrovsky: About life? It is about the role of liquid crystals in biology?

Boris Dolgin: Yes.

Alexey Bobrovsky: Unfortunately, this is not my topic at all. I will link to the book at the end. First of all, when they talk about the connection of liquid crystals in biology, they talk about how they can be used in medicine - there are a lot of different options. In lipid cell membranes, the liquid-crystalline state takes place at reasonable biological temperatures.

Boris Dolgin: And this is not an artifact entirely, and this is an additional study.

Alexey Bobrovsky: Yes. It seems to me that the role of the liquid crystal state is still not really known, and sometimes there is evidence that DNA in a cell can exist in a liquid crystal state, but this is a topic for future research. This is not my field of study. I am more interested in liquid crystal synthetic polymers, which I will continue to talk about.

Boris Dolgin: Are LC polymers completely artificial?

Alexey Bobrovsky: Yes, basically everything is artificial. The coloration, for example, of some beetles and butterflies is due to such natural not liquid crystals, but a frozen liquid crystalline state due to chitinous biological polymers. So the evolution was distributed, that the coloring is not due to pigments, but due to the cunning structure of polymers.

Mikhail Potanin A: I have a question about the magnetic sensitivity of liquid crystals. How sensitive are they to the Earth's magnetic fields? Can they make compasses?

Alexey Bobrovsky: No. Unfortunately, it happened. What determines the sensitivity of liquid crystals? There is the concept of diamagnetic susceptibility and permittivity, and in the case of an electric field, everything is much more convenient and better, that is, it is enough to really apply 1 V to such a liquid crystal cell - and everything will be reoriented, and in the case of a magnetic field, we are talking about teslas - such field strengths incomparably higher than the strength of the Earth's magnetic field,

Lev Moskovkin: I may have a completely amateurish question. The lecture is absolutely charming, the aesthetic satisfaction is great, but the presentation itself is smaller. The pictures you showed resemble the core - they are also aesthetically active - and the Jabotinsky reaction, although your pictures are not cyclical. Thank you.

Alexey Bobrovsky A: I'm not ready to answer this question. This needs to be looked at in the literature. In polymers and liquid crystals there is a theory of "scaling" (scaling), that is, self-similarity. I find it difficult to answer this question, I am not competent in this topic.

Natalia: Now they are awarding Nobel Prizes to Russian scientists. In your opinion, Fredericks, if he had survived, could have received this award? In general, did any of the scientists who dealt with this topic receive the Nobel Prize?

Alexey Bobrovsky A: I think, of course, Fredericks would be the first candidate. He died in a camp during the war. If he had lived until 1968-1970, then he would have been the first candidate for the Nobel Prize - this is quite obvious. Still a great physicist, but was not awarded (we are talking about our scientists), - Tsvetkov - the founder of the school of physicists in St. Petersburg, unfortunately, it fell apart to one degree or another. The question of who received the Nobel Prize for liquid crystals was not specifically considered or studied, but, in my opinion, only Paul de Gennes received the Nobel Prize for polymers and liquid crystals.

Boris Dolgin: Has the fashion for the study of liquid crystals gone forever?

Alexey Bobrovsky: Yes, of course, there is no hype, because a lot is already clear with the simplest mesophase (nematic liquid crystal phase), and it is clear that it is the most optimal for use. There is still some interest in more complex phases, because one can get some advantages over the well-studied one, but the number of publications on the liquid crystal state is declining.

Boris Dolgin: That is, you do not see any qualitative leaps in understanding, no zones where there would be a global mystery.

Alexey Bobrovsky: I think it's better not to predict, because anything can happen. Science does not always develop consistently. Sometimes there are strange jumps, so I do not undertake to make any predictions.

Konstantin Ivanovich: I would like to know how safe they are for human life.

Alexey Bobrovsky A: The people who make LCDs are tested for safety. If you drink a liter of liquid crystal, then it will probably become bad, but since milligrams are used, then there is no serious danger. It's much safer than broken, leaking mercury from a thermometer. It's completely incomparable in damage. Now there are studies on the utilization of liquid crystals. I've heard one report where this issue is being taken seriously, that there's already a lot of scrap and how it can be reclaimed, but the environmental issues are minimal. They are safe.

Boris Dolgin: There was a very interesting thing at the end. If you imagine a used LCD monitor and so on. What will happen to him next, what happens? How is it disposed of - or not disposed of, or somehow decomposed, or remains?

Alexey Bobrovsky: I think that liquid crystal molecules are the first thing that will decompose under the action of external influences.

Boris Dolgin: That is, there is no special specificity here?

Alexey Bobrovsky: Of course not. I think the problems with the recycling of plastics and polymers are much more complicated there.

Oleg: Tell me, please, what determines the temperature range of liquid-crystal phases? As you know, all modern displays operate at a very wide temperature range. How did you manage to achieve this, and what properties and structure of matter determine them?

Alexey Bobrovsky: Great question. Indeed, ordinary compounds, most of the organic compounds that are synthesized individually, have temperatures such as I have shown, cholesteryl benzoate melts at 140°, then isotropic decomposition 170°. There are individual substances that have a low melting point, near room temperature, and transform into an ordinary isotropic liquid in the region of 50°, but in order to realize such a wide temperature range, down to sub-zero temperatures, mixtures had to be made. Conventional mixed compositions of different substances, when mixed, their melting point is greatly reduced. Such a trick. Usually these are homologous series, what is used in displays is a biphenyl derivative, where there is no X and a nitrile substituent, and tails of different lengths are taken as alkyl tails, and a mixture of 5-7 components makes it possible to lower the melting point below 0 °, while leaving the temperature of enlightenment, that is, the transition of the liquid crystal to the isotropic phase, above 60 °, - this is such a trick.

Lecture text. Part 2

First of all, I would like to say what polymers are.

Polymers are compounds that are obtained by repeated repetition, that is, by chemical bonding of identical units - in the simplest case, identical, as in the case of polyethylene, these are CH 2 units interconnected in a single chain. Of course, there are more complex molecules, up to DNA molecules, whose structure does not repeat itself, is organized in a very complex way.

The main types of polymer topology: the simplest molecules are linear chain molecules, there are branched, comb-shaped polymers. Comb polymers have played an important role in the production of liquid crystal polymers. The star-shaped, linked rings of polycatenanes are the most diverse molecular shapes. When the liquid crystal state was being studied with might and main, when liquid crystals were being studied, an idea arose: is it possible to combine the unique optical properties of liquid crystals with the good mechanical properties of polymers - the ability to form coatings, films, some products? And what came to mind in 1974 (there was the first publication) - in the late 60s - early 70s, they began to offer different approaches to the production of liquid crystal polymers.

One of the approaches is to bind rod-shaped, stick-shaped molecules to a linear macromolecule, but it turned out that such polymers do not form a liquid-crystal phase, they are ordinary fragile glasses that, when heated, begin to decompose and give nothing. Then, in parallel, in two laboratories (I will talk about this in more detail later), an approach was proposed for attaching such rod-shaped molecules to the main polymer chain through flexible spacers - or decoupling, in Russian. And then it turns out the following: there is a small autonomy between the main polymer chain, it goes largely independently, and the behavior of rod-shaped molecules, that is, the main polymer chain does not interfere with the formation of a liquid crystal phase by rod-shaped fragments.

This approach turned out to be very fruitful, and in parallel in two laboratories - in the laboratory of Nikolai Alfredovich Plate in the Soviet Union and in the laboratory of Ringsdorf - such an approach was independently proposed, and I am happy to work now in the laboratory of Valery Petrovich Shibaev at the Faculty of Chemistry of Moscow State University, that is, I work in the laboratory where it was all invented. Naturally, there were disputes about priorities, but it doesn't matter.

The main types of liquid crystal polymers. I won't talk about such main chain or backbone groups (that's one type of polymer), I'll talk mainly about comb-shaped liquid crystal polymers, in which rod-shaped fragments are connected to the main chain through a flexible aliphatic decoupling.

An important advantage of the approach to the creation of liquid crystal polymers in terms of synthesis and combination of different properties is the possibility of obtaining homopolymers. That is, a monomer is taken that is capable of forming a chain molecule, for example, due to the double bond shown schematically here, and you can get a homopolymer, that is, a polymer whose molecules consist of the same rod-shaped fragments, or you can make copolymers by combining two different fragments, - they can both form a mesophase, or non-mesogenic fragments can be combined with mesogenic fragments, and it turns out that we have the ability to chemically force heterogeneous components to be in one polymer system. In other words, if they tried to mix such a monomer with such a monomer without chemical bonding, they would give two separate phases, and by binding them chemically, we force them to be in one system, and then I will show how good it is.

An important advantage and difference between polymer liquid crystals and low-molecular liquid crystals is the possibility of forming a glassy state. If you look at the temperature scale, we have an isotropic phase at high temperatures, when the temperature drops, a liquid crystalline phase forms (under these conditions, the polymer looks like a very viscous liquid), and when cooled, a transition to a glassy state is observed. This temperature is usually close to room temperature or slightly above room temperature, but this depends on the chemical structure. Thus, in contrast to low-molecular compounds, which are either liquid or pass into a crystalline state, the structure changes. In the case of polymers, this structure is frozen in a glassy state that can persist for decades, and this is important from the point of view of application, let's say for the recording of information storage, we can change the structure and orientation of the molecule, fragments of the molecule and freeze them at room temperature. This is an important difference and advantage of polymers from low molecular weight compounds. What else are polymers good for?

This video demonstrates a liquid crystal elastomer, that is, it feels like an elastic band that shrinks when heated and expands when cooled. This work is taken from the Internet. This is not my work, here is an accelerated image, that is, in reality, unfortunately, this transition is observed for tens of minutes. Why is this happening? What is a liquid crystal elastomer, which has a sufficiently low glass transition temperature, that is, it is in an elastic state at room temperature, but the macromolecules are cross-linked, and if we synthesize a film in the liquid crystal phase, then the polymer chain slightly repeats the orientation of mesogenic groups, and if we If we heat it, then the mesogenic groups pass into a disordered state and, accordingly, transfer the main polymer chains into a disordered state, and the anisometry of macromolecular coils changes. This leads to the fact that during heating, during the transition from the mesophase to the isotropic phase, a change in the geometric dimensions of the sample is observed due to a change in the shape of the polymer coils. In the case of low-molecular liquid crystals, this cannot be observed. Two groups in Germany, Finkelmann, Zentel, and other groups were doing a lot of these things. The same can be observed under the influence of light.

There are a lot of works on photochromic polymers that contain an azobenzene fragment - two benzene rings linked by an NN-double bond. What happens when such molecular fragments are exposed to light? The so-called trans-cis isomerization is observed, and the rod-shaped fragment, when irradiated with light, changes into a beveled curved cis-form, a curved fragment. This also leads to the fact that the order in the system drops significantly, and as we saw earlier during heating, also during irradiation there is a reduction in geometric dimensions, a change in the shape of the film, in this case we observed a reduction.

Various kinds of bending deformations can be realized during irradiation, i.e., such bending of the film can be realized when irradiated with UV light. When exposed to visible light, reverse cis-trans isomerization is observed and this film expands. All sorts of options are possible - this may depend on the polarization of the incident light. I am talking about this because it is now a fairly popular area of ​​research in liquid crystal polymers. They even manage to make some devices based on this, but so far, unfortunately, the transition times are quite long, that is, the speed is low, and therefore it is impossible to talk about any specific use, but, nevertheless, these are such artificially created muscles, which act, work when the temperature changes or when exposed to light of different wavelengths. Now I would like to talk a little about my work directly.

What is the purpose of my work, our laboratory. I have already spoken about the advantage of copolymerization, about the possibility of combining completely dissimilar fragments in one polymer material, and the main task, the main approach to creating such different multifunctional liquid crystal polymers, is the copolymerization of a variety of functional monomers that can be mesogenic, that is, responsible for the formation of a liquid crystal phases, chiral (I will talk about chirality later), photochromic, that is, they are able to change under the influence of light, electroactive, which carry a large dipole moment and can reorient under the action of the field, various kinds of functional groups that can, for example, interact with metal ions, and material variations are possible. And this is such a hypothetical comb-shaped macromolecule here, but in reality we get double or ternary copolymers that contain different combinations of fragments, and, accordingly, we can change the optical and other properties of these materials with different influences, for example, light and electric field. One such example is the combination of chirality and photochromism.

I have already spoken about the cholesteric mesophase - the fact is that a helical molecular structure is formed with a certain helix pitch, and such systems have a selective reflection of light due to such periodicity. This is a schematic drawing of a film section: a certain spiral pitch, and the fact is that selective reflection is linearly related to the spiral pitch - proportional to the spiral pitch, that is, by changing the spiral pitch in one way or another, we can change the color of the film, the wavelength of selective reflection. What causes such a structure with a certain degree of twist? For such a structure to form, it is necessary to introduce chiral fragments into the nematic phase.

Molecular chirality is the property of molecules to be incompatible with their mirror image. The simplest chiral fragment we have in front of us is our two palms. They are roughly a mirror image of each other and are not comparable in any way. Molecular chirality introduces into the nematic system the ability to twist, to form a helix. It must be said that there is still no intelligible, well-explaining theory of spiral twisting, but, nevertheless, it is observed.

There is an important parameter, I will not dwell on it, - this is the twisting force, and it turned out that the twisting force - the ability of chiral fragments to form a helical structure - strongly depends on the geometry of chiral fragments.

We have obtained chiral-photochromic copolymers that contain a mesogenic fragment (depicted by a blue rod) - it is responsible for the formation of a liquid-crystal phase of the nematic type. Copolymers with chiral-photochromic fragments were obtained, which, on the one hand, contain a chiral molecule (group), and, on the other hand, a fragment that is capable of photoisomerization, that is, to change the geometry under the action of light, and by irradiating such molecules, we induce trans -cis-isomerization, we change the structure of the chiral photochromic fragment and - as a result - its ability to induce the efficiency of inducing a cholesteric helix, that is, in this way we can, for example, unwind the cholesteric helix under the action of light, we can do it reversibly or irreversibly. What does the experiment look like, what can we implement?

We have a section of a cholesteric film of a cholesteric polymer. We can irradiate it using a mask and locally induce isomerization, during isomerization, the structure of chiral fragments changes, their twisting ability decreases and helix unwinding is observed locally, and since helix unwinding is observed, we can change the wavelength of selective reflection of color, that is, color films.

The samples that were obtained in our laboratory are polymer samples irradiated through a mask. We can record various kinds of images on such tapes. This may be of applied interest, but I would like to note that the main emphasis in our work is the study of the influence of the structure of such systems on molecular design, on the synthesis of such polymers, and on the properties of such systems. In addition, we have learned not only to control light, the wavelength of selective reflection, but also to control electricity. For example, we can record some kind of color image, and then, by applying an electric field, somehow change it. Due to the versatility of such materials. Such transitions - unwinding-spinning of the spiral - can be reversible.

It depends on the specific chemical structure. For example, we can cause the wavelength of selective reflection (in fact, color) to depend on the number of write-erase cycles, that is, when exposed to ultraviolet light, we unwind the spiral, and the film turns from green to red, and then we can heat it at a temperature of 60 ° and induce reverse spin. In this way, many cycles can be realized. In conclusion, I would like to return a little to the aesthetic aspect of liquid crystals and liquid crystal polymers.

I showed and talked a little about the blue phase - a complex, very interesting structure, they are still being studied, nanoparticles are introduced there and they look at what changes there, and in low molecular weight liquid crystals this phase exists in some fractions of degrees (2 ° -3 °, but no more), they are very unstable. It is enough to slightly push the sample - and this beautiful texture, an example of it is shown here, is destroyed, and in polymers in 1994-1995, by heating the films for a long time, firing at certain temperatures, I managed to see such beautiful textures of cholesteric blue phases, and I succeeded without no tricks (without using liquid nitrogen) just cool these films and observe these textures. More recently, I found these samples. Already 15 years have passed - and these textures have remained absolutely unchanged, that is, the cunning structure of the blue phases, like some ancient insects in amber, has remained fixed for more than 10 years.

This, of course, is convenient from the point of view of research. We can put it in an atomic force microscope, study sections of such films - it's convenient and beautiful. That's all for me. I would like to refer to the literature.

The first book by Anatoly Stepanovich Sonin, I read it more than 20 years ago, in 1980, published by the Centaur and Nature publishing house, then, while still a schoolboy, I became interested in liquid crystals, and it so happened that Anatoly Stepanovich Sonin was a reviewer of my thesis. A more modern publication is an article by my scientific adviser Valery Petrovich Shibaev "Liquid crystals in the chemistry of life." There is a huge amount of English-language literature; If there is interest and desire, you can find a lot of things yourself. For example, Dirking's book Liquid Crystal Textures. Recently I found a book that focuses on the application of liquid crystals in biomedicine, so if someone is interested in this particular aspect, then I recommend it. There is an e-mail for communication, I will always be happy to answer your questions and maybe send some articles if there is such an interest. Thank you for your attention.

Lecture discussion. Part 2

Alexey Bobrovsky: It was necessary to show some specific chemistry. This is my omission. No, this is a multi-stage organic synthesis. Some simple substances are taken, in flasks it resembles chemical cuisine, molecules in the course of such reactions are combined into more complex substances, they are released at almost every stage, they are analyzed somehow, the agreement of the structure that we want to obtain is established with those spectral data that the instruments give us, so that we can be sure that this is the substance that we need. This is a rather complex sequential synthesis. Of course, liquid crystal polymers are even more labor-intensive synthesis to obtain. It looks like orange powders are made from various white powders. The liquid crystal polymer looks like an elastic band, or it is a solid sintered substance, but if you heat it, make a thin film (when heated, this is possible), then this incomprehensible substance gives beautiful pictures in a microscope.

Boris Dolgin: I have a question, maybe from another sphere, in fact, maybe first Leo, then me, so as not to divert from the actual part.

Lev Moskovkin: You really fascinated me with today's lecture, for me this is the discovery of something new. The questions are simple: how big is the muscle strength? What does he work for? And out of ignorance, what is texture, how does it differ from structure? After your lecture, it seems to me that everything that is arranged in life, everything due to liquid crystals, there is also much regulated by light and a weak impulse. Thank you very much.

Alexey Bobrovsky A: Of course, it cannot be said that everything is regulated by liquid crystals, of course it is not. There are different forms of self-organization of matter, and the liquid-crystal state is only one of such forms of self-organization. How strong are polymer muscles? I don’t know the quantitative characteristics, compared to the existing iron-based devices, roughly speaking, of course, they are not so strong, but I want to say that modern bulletproof vests, for example, contain Kivlar material - a fiber that has a liquid crystal structure main chain type, polymer with mesogenic groups in the main chain. During the production of this fiber, the macromolecules are drawn along the direction of the draw and a very high strength is provided, this makes it possible to make strong fibers for body armor, actuators, or muscles under development, but very weak forces can be achieved there. The difference between texture and structure. Texture is a concept that is used by people who are engaged in carpets, design of things, some visual things, artistic design, that is, first of all, it is a look. Luckily, the texture of liquid crystals, that is, the characteristic picture, helps a lot in determining the structure of a liquid crystal, but these are, in fact, different concepts.

Oleg Gromov, : You said that there are polymer liquid crystal structures that have a photochromic effect and electrical and magnetic sensitivity. The question is. It is also known in mineralogy that Chukhrov described liquid-crystalline formations of inorganic composition in the 50s, and it is known that there are inorganic polymers, respectively, the question is: do inorganic liquid-crystalline polymers exist, and if so, is it possible for them to perform these functions, And how are they implemented in this case?

Alexey Bobrovsky: The answer is rather no than yes. Organic chemistry, the property of carbon to form a variety of different compounds, made it possible to carry out a colossal design of various kinds of low-molecular liquid crystals, polymer compounds, and, in general, therefore, we can talk about some kind of diversity. These are hundreds of thousands of substances of low molecular weight polymers, which can give a liquid crystalline phase. In the case of inorganic polymers, I don't know, the only thing that comes to mind is some suspensions of vanadium oxide, which also seem like polymers, and their structures are usually not exactly established, and this is at the research stage. It turned out to be a little away from the main scientific "mainstream", when everyone is working on the design of ordinary organic liquid crystals, and there really can be formations of lyotropic liquid crystal phases, when the phase is induced not by a change in temperature, but primarily by the presence of a solvent, that is, these are usually nanocrystals necessarily elongated shape, which due to the solvent can form an orientational order. Specially prepared vanadium oxide gives this. Other examples, perhaps, I do not know. I know that there are several such examples, but to say that this is a polymer is not entirely correct.

Oleg Gromov, Institute of Biochemistry and Analytical Chemistry of the Russian Academy of Sciences: And how then to consider the liquid crystal formations discovered by Chukhrov and others in the 50s?

Alexey Bobrovsky: I don't know, unfortunately, this area is far from me. As far as I know, it seems to me that it is impossible to speak for sure about the liquid crystalline state, because the word "liquid", to be honest, is not applicable to polymers that are in a glassy state. It is incorrect to say that this is a liquid crystal phase, it is correct to say "frozen liquid crystal phase". Probably, similarity, a degenerate order, when there is no three-dimensional order, but there is a two-dimensional order - this is probably a general phenomenon, and if you search, you can find a lot where to find it. If you send links to such works to my e-mail, I will be very grateful.

Boris Dolgin: It is very good when one manages to become another platform where scientists of different specialties can keep in touch.

Alexey Bobrovsky: It's great

Voice from the hall: Another amateurish question. You said that photochromic liquid crystal polymers have a relatively slow response to a change in the environment. What is their approximate speed?

Alexey Bobrovsky: We are talking about a response within minutes. In the case of strong light exposure to very thin films, people achieve a second response, but so far this is all slow. There is such a problem. There are effects that are related to something else (I did not talk about this): we have a polymer film, and there are photochromic fragments in it, and we can act with polarized light of sufficient intensity, and this light can cause rotational diffusion, that is, the rotation of these molecules perpendicular to the plane of polarization - there is such an effect, it was discovered long ago initially, now it is also being investigated, and I am also doing this. With a sufficiently high light intensity, effects can be observed within milliseconds, but usually this is not associated with a change in the geometry of the film, it is inside, first of all, the optical properties change.

Alexey Bobrovsky: There was an attempt to make material for recording information, and there were such developments, but, as far as I know, such materials cannot compete with the existing magnetic recording, other inorganic materials, so interest has somehow died out in this direction, but this does not mean that it won't restart again.

Boris Dolgin: The emergence of, say, new requirements due to something.

Alexey Bobrovsky: The utilitarian side of things does not interest me too much.

Boris Dolgin: My question is partly related to it, but not about how you can use it, it is a bit organizationally utilitarian. In the area in which you work at your department and so on, you, as far as we have said, have joint projects, orders from some business structures, and so on. How is interaction organized in this area in general: a scientist-researcher, relatively speaking, an inventor / engineer or an inventor, and then an engineer, maybe different subjects, then, relatively speaking, some kind of entrepreneur who understands what to do with it, maybe, but this is unlikely, an investor who is ready to give money to an entrepreneur so that he can implement this, as they say now, innovative project? How is this chain arranged in your environment to the extent that you somehow came into contact with it?

Alexey Bobrovsky: So far there is no such chain, and whether there will be one is unknown. In principle, the ideal form of funding is the way conventional fundamental science is funded. If we take the RFBR as a basis and everything that has been discussed many times, because personally I would not want to do something so applied, an order.

Boris Dolgin: That's why I'm talking about different subjects and in no case do I say that a scientist should be both an engineer and an entrepreneur, and so on. I'm talking just about different subjects, about how interaction can be set up, how, perhaps, interaction is already working.

Alexey Bobrovsky A: We have various proposals from outside, but these are mainly companies from Taiwan, Korea, from Asia, for various kinds of work related to the use of liquid crystal polymers for various display applications. We had a joint project with Philips, Merck and others, but this is within the framework of a joint project - we are doing part of some research work, and such an intellectual output or output in the form of polymer samples either has a continuation or does not, but most often ends with an exchange of opinions, some kind of scientific development, but this has not yet reached any application. Seriously, you can't say.

Boris Dolgin: You are commissioned for a kind of research, the development of some option, some idea.

Alexey Bobrovsky: In general, yes, this happens, but I don’t like this form of work (my personal feeling). Whatever came to my mind, I do as much as possible, and not so that someone said: "Make such and such a film with such properties." I'm not interested.

Boris Dolgin: Imagine a person who is interested. How could he, he, who is interested in refining your general scientific ideas that you received from your altruistic, actually scientific interest, how could he interact with you in such a way that it would be really interesting for both of you? What is the organizational chart?

Alexey Bobrovsky: I find it difficult to answer.

Boris Dolgin: General seminars? What could it be? There are no such attempts - some kind of engineers? ..

Alexey Bobrovsky: Within the framework of a joint project, everything can be realized. Some kind of interaction is quite possible, but I probably did not quite understand the question, what is the problem?

Boris Dolgin: So far, the problem is the lack of interaction between different types of structures. It comes down on you as a scientist, or it comes down to doing things that you might not want to do. This is the problem.

Alexey Bobrovsky: It is a problem of colossal underfunding

Boris Dolgin: Imagine that there will be additional funding, but the need for technical development will not disappear from this. How can you move from you to technology in a way that satisfies you?

Alexey Bobrovsky: The fact is that modern science is quite open, and what I do, I publish - and the sooner the better.

Boris Dolgin: So you are ready to share the results, hoping that those who have a taste can take advantage of this?

Alexey Bobrovsky: If someone reads my article and he has some idea, yes, I will only be grateful. If specific developments come out of this publication, there will be patents, money, but for God's sake. In this form, I would be glad, but, unfortunately, in reality it turns out that everything exists in parallel, there is no such way out. The history of science shows that there is often a delay in a specific application after some fundamental discovery - big or small.

Boris Dolgin: Or after some request.

Alexey Bobrovsky: Or so.

Lev Moskovkin: I have a slightly provocative question. The topic that Boris raised is very important. Is there the influence of a certain fashion here (this was heard at one of the lectures on sociology)? You said that it is not fashionable to deal with liquid crystals now. This does not mean that since they are not being dealt with, then they are not needed, maybe this interest will return, and most importantly ...

Boris Dolgin: That is, Leo brings us back to the question of the mechanisms of fashion in science as in a certain scientific community.

Lev Moskovkin: In fact, Tchaikovsky also spoke about this, where fashion is extremely strong in all sciences. The second question: I know very well how authorities in science were chosen who were able to generalize. You can publish your materials as much as you like, I personally never come across them, for me this is a whole layer that I simply did not know. To generalize in such a way as to understand the value of this for understanding the same life, for understanding what else we can do. Thank you.

Boris Dolgin: I did not understand the second question, but let's deal with the first one for now - about fashion in science. What is the mechanism of why it is not fashionable now, is there any danger in it?

Alexey Bobrovsky: I don't see any danger. It is clear that issues related to funding are important, but, nevertheless, it seems to me that in many respects science now rests on specific people who have specific personal interests, an interest in this or that problem. It is clear that the conditions dictate some restrictions, however, the activity of specific people leads to the fact that a certain area develops, as everything develops. Despite the fact that much is said about the fact that science has become collective. Indeed, now there are big projects, sometimes quite successful, but, nevertheless, the role of the individual in the history of science is huge even now. Personal likes and interests play an essential role. It is clear that, as in the case of liquid crystals, this development of electronics served as a great impetus for the development of liquid crystal research, when they realized that liquid crystals can be used and make money from it, naturally, a lot of money went into research. It is clear that such a connection ...

Boris Dolgin: Feedback from business and science.

Alexey Bobrovsky: ...this is one of the features of modern science, when an order comes from people who earn money and produce a product - and then research is funded, and, accordingly, there is a shift in emphasis from what is interesting to what is profitable. It has its pros and cons, but that's the way it is. Indeed, now interest in liquid crystals has gradually dried up, because everything that could be pulled out is already being produced, and something remains to be improved. I don’t know, I never seriously thought about it, nevertheless, there are various kinds of display applications, in optoelectronics applications of liquid crystals (people are working on this), as sensors, up to the fact that work is underway on the possibility of using liquid crystals as a biological sensor. molecules. So, in general, I think that interest will simply not dry up, in addition, a large wave of research is related to the fact that they began to give money for nano. In principle, there is, despite the fact that it is such a popular fashion - to put nanoparticles into liquid crystals, the number of works is large, but among them there are good interesting works related to this topic, that is, what happens to nano-objects when they enter a liquid crystal medium what effects appear. I think that development is possible in terms of obtaining all sorts of different complex devices, which is associated with the appearance of metamaterials that have very interesting optical properties - these are unusual structures that are made in various ways in combination with liquid crystals, new optical effects and new applications are possible . I am now reviewing articles in the journal Liquid Crystals, and their level is dropping, and the number of good articles is decreasing, but this does not mean that everything is bad, and the science of liquid crystals will not die, because this is a very interesting subject. The drop in interest does not look like a catastrophe to me.

Boris Dolgin: Here we quietly move on to the second question asked to us by Leo. If some kind of fundamentally new theory is born on the basis of the existing one, promising something plus for liquid crystals, apparently, interest will immediately increase.

Alexey Bobrovsky: It is possible that this will happen.

Boris Dolgin: As far as I understand the question, this is what we are talking about, there are intra-scientific texts that gradually change something in understanding, there are innovative texts that change radically, but at the same time a kind of interface between specialists and society, perhaps consisting of the same scientists , but from other areas, there are some generalizing works that explain to us how to solder these pieces into some kind of overall picture. As I understand it, Leo told us about this, asking how one chooses, and who writes these generalizing works?

Alexey Bobrovsky: There is such a concept - scientific journalism, which is not very developed in our country, but it exists all over the world, and I can imagine how well it is developed there, and, nevertheless, it also exists in our country. The current public lecture also points to this.

Boris Dolgin: It cannot be said that someone specifically closes the scope of work.

Alexey Bobrovsky: No, no one closes anything, on the contrary, all normal scientists try their best to show the world what they have done: as quickly and as accessible as possible to the best of their abilities. It is clear that someone can tell well, and someone badly, but for this there are scientific journalists who can serve as a transmitter of information from scientists to society.

Boris Dolgin: Back in Soviet times, there was popular science literature, and there was still a special genre - scientific literature, partly collections of "Ways into the Unknown" in the early 60s, books of the "Eureka" series, one of the first post-war pioneers was Daniil Danin who wrote mainly about physics. Another question is that there are still scientists who write some generalizing works, popularizing something for someone, but hardly anyone chooses who will write and whom to read or not to read. The mentioned Tchaikovsky writes something, someone likes it.

Alexey Bobrovsky: The problem, I think, is the following. The fact is that in our country there are now catastrophically few normal scientists, and the state of science in itself is nowhere worse. If we talk about liquid crystals and liquid crystal polymers, then these are single laboratories that are already dying. It is clear that in the 90s there was some kind of collapse and nightmare, but, in general, we can say that there is no science of liquid crystals in Russia. I mean - the scientific community, it turns out that I communicate more often with people who work abroad, read articles and all that, but there are practically no articles coming from us. The problem is that we do not have science, and not that there are no generalizing works in this science. It is possible to generalize what is happening in the West - that is also fine, but there is no basis, an important link, there are no scientists.

Lev Moskovkin: I'll clarify, although in principle everything is correct. The fact is that we are always revolving around the topic of the last lecture. The competition in science between scientists is so strong that I am categorically flattered that I saw it with my own eyes, and I agree that every scientist strives to show the world his achievements. This is available only to someone who is a recognized authority, like Timofeev-Resovsky. This was done in Soviet times - it’s known how - and here comes the effect, an example that, perhaps, will explain a lot - the effect of a green notebook that was published in hell knows where, and no one can remember the name of this supernumerary conference, because no one A journal accredited by the VAK now, an academic journal would not accept such novelty in principle, but it gave birth to a new science, it turned into the science of genetics, into an understanding of life, and this, in general, is now already known. It was in Soviet times with support from above - Timofeev-Resovsky was supported at the plenum of the Central Committee of the CPSU from the competition of colleagues, otherwise he would have been eaten.

Boris Dolgin: The situation when the state finished off a significant part of science: without the support of other bases of the state it was impossible to escape.

Lev Moskovkin: In genetics, there is an avalanche of data that there is no one to generalize, because no one trusts anyone and no one recognizes someone else's authority.

Boris Dolgin: Why?! We had geneticists who listened to other geneticists, and they discussed with pleasure.

Alexey Bobrovsky: I do not know how it happens in genetics, but in the science that I do, the situation is completely opposite. People who get a new interesting result immediately try to publish it as soon as possible.

Boris Dolgin: At least from the interests of competition - to stake out a place.

Alexey Bobrovsky: Yes. It is clear that they may not write some details of the methods and so on, but usually, if you write an e-mail, ask how you did it there, it's just very interesting, it's all quite open - and ...

Boris Dolgin: According to your observations, science is becoming more open.

Alexey Bobrovsky: At least I live in the era of open science, and that's good.

Boris Dolgin: Thanks. When molecular biologists spoke with us, they usually referred to quite openly lying bases and so on, recommended to apply.

Alexey Bobrovsky: In physics, there is the same thing, there is an archive when people can post a raw (controversial) version of an article even before passing the review, but here there is more a struggle for the speed of publications than faster priority for those. I don't see any closure. It is clear that this has nothing to do with the closed military and others, I'm talking about science.

Boris Dolgin: Thanks. More questions?

Voice from the hall: I don't have a question, but a suggestion, an idea. It seems to me that this theme of crystallization pictures has a lot of potential for stories about science to children and young people in schools. Maybe it makes sense to create one e-lesson, lasting 45 minutes, and distribute it to secondary schools? Now there are electronic boards that many do not use, they were ordered to have them in schools. I think it would be nice to show these pictures to children for 45 minutes, and then, at the end, explain how it's all done. It seems to me that it would be interesting to propose such a topic, somehow finance it.

Alexey Bobrovsky: I'm ready to help, if anything. Provide, write what you need.

Boris Dolgin: Amazing. This is how generalizations are formed, this is how it is ordered. Good. Thanks a lot. Any other creative questions? Maybe someone was missed, we don’t see, in my opinion, we basically discussed it.

Boris Dolgin A: There are scientists, there is no science.

Boris Dolgin: That is, is it a necessary or necessary and sufficient condition?

Alexey Bobrovsky: Yes, the damage is irreversible, time has been lost, it is quite obvious, and, of course, it sounds: “How is it that there is no science in Russia ?! How it is? This cannot be, there is science, there are scientists, there are articles.” First, in terms of level, I read scientific journals daily. Very rarely come across articles by Russian authors, made in Russia, on liquid crystals or polymers. This is because either nothing is happening, or everything is happening at such a low level that people are not able to publish it in a normal scientific journal, of course, no one knows them. This is an absolutely terrible situation.

Alexey Bobrovsky: More and more.

Boris Dolgin: That is, the problem is not in the authors, the problem is in science.

Alexey Bobrovsky: Yes, that is, of course, there is no perfect, well-functioning structure in Russia, or at least somehow working under the name "Science". Fortunately, there is an openness of laboratories that work more or less at a normal level and are involved in the general scientific process of international science - this is the development of communication capabilities via the Internet, in other ways, the openness of borders allows you not to feel separated from the global scientific process, but inside the country there is so that, of course, there is not enough money, and if funding is increased, this is unlikely to change anything, because in parallel with an increase in funding, it is necessary to have the opportunity to examine those people who are given this money. You can give money, someone will steal it, spend it on who knows what, but the situation will not change in any way.

Boris Dolgin A: Strictly speaking, we have a chicken and egg problem. On the one hand, we will not create science without funding, on the other hand, with funding, but without the scientific community, which will provide a market for expertise, ensure normal reputations, we will not be able to give this money in a way that will help science.

Alexey Bobrovsky: In other words, it is necessary to attract international expertise, assessments from strong scientists, regardless of their country of residence. Naturally, it is necessary to switch to English for attestation cases related to the defense of candidate, doctoral; at least abstracts must be in English. This is quite obvious, and there will be some movement in this direction, maybe it will somehow change for the better, and so - if you give everyone money ... naturally, strong scientists who will get more money - they, of course, will work more efficiently , but most of the money will disappear to no one knows where. This is my opinion.

Boris Dolgin: Tell me, please, you are a young scientist, but you are already a doctor of sciences, and young people come to you in a different sense, students, younger scientists. Are there those who follow you?

Alexey Bobrovsky: I work at the University, and willy-nilly, sometimes I want it, sometimes I don't want it, I supervise coursework, diploma and postgraduate work.

Boris Dolgin: Are there future scientists among them?

Alexey Bobrovsky: Has already. There are quite successfully working people whom I supervised, diploma works, for example, who are postdocs or heads of scientific groups, of course, we are talking only about abroad. Those that I led and they remained in Russia, they do not work in science, because they have to feed their families, live normally.

Boris Dolgin A: Thank you, that is finance.

Alexey Bobrovsky: Naturally, funding, salaries do not stand up to scrutiny.

Boris Dolgin: It's still private...

Alexey Bobrovsky: There is no secret in this. The rate of a senior researcher with a candidate's minimum at the University is fifteen thousand rubles a month. Everything else depends on the activity of the scientist: if he is able to have international grants, projects, then he gets more, but he can count on fifteen thousand rubles a month.

Boris Dolgin: What about a PhD?

Alexey Bobrovsky: They haven’t set me yet, I still don’t know exactly how much they will give, plus four thousand more will be added.

Boris Dolgin: The mentioned grants are quite an important thing. Only today we have published news sent by an interesting researcher, but when the question of funding was asked, she spoke, in particular, about the importance of this area, and again, not to mention our publications, Minister Fursenko says that scientific supervisors should grants to finance their graduate students and thus financially motivate them.

Alexey Bobrovsky: No, this is how it usually happens in a good scientific group, if a person, like Valery Petrovich Shibaev, head of the laboratory in which I work, has a well-deserved name in the scientific world, there is an opportunity for grants, projects. More often than not, I don’t find myself at a “naked” rate of fifteen thousand, there are always some projects, but not everyone can, this is not a general rule, which is why everyone leaves.

Boris Dolgin: That is, the leader must have a sufficiently high international authority and, moreover, be in the stream.

Alexey Bobrovsky A: Yes, most of the time. I think I've been lucky in many ways. The element of getting into a strong scientific group worked in a positive way.

Boris Dolgin: Here we see the feedback of the good old science, that this most powerful scientific group arose, due to which you were able to realize your trajectory. Yes, that's very interesting, thanks. I ask for the last word.

Voice from the hall: I do not pretend to have the last word. I want to note that what you are talking about is absolutely understandable, and do not take it as a sport. I want to note that in the lecture by Alexei Savvateev it was said that there is no science at all in America. His point of view is as convincingly argued as yours. On the other hand, in Russia, science developed especially rapidly when science did not pay at all, but actively stole, there was such a thing.

Boris Dolgin: Are we talking about the end of the 19th - beginning of the 20th century?

Boris Dolgin: In Germany?

Boris Dolgin: And when he more actively developed his scientific ...

Voice from the hall: In Russia, not his, but in Russia in general, science developed most effectively when they did not pay. There is such a phenomenon. I can justify, this is not a point of view, Boris, this is a fact. I also want to tell you quite responsibly - this is no longer a fact, but a conclusion - that your hopes that international expertise and the English language will help you are futile, because, working in the Duma, I see fierce competition for ownership and lobbying in Duma unilateral copyright laws towards America. They all attribute a huge percentage of intellectual property, they are not at all interested in our weapons not being copied there, they do it themselves.

Boris Dolgin: I see, the problem is...

Alexey Bobrovsky: Weapons and science are parallel things.

Voice from the hall: The last example: the fact is that when Zhenya Ananiev, we studied together at the biological faculty, discovered mobile elements in the Drosophila genome, then recognition came only after publication in the Chromosomes magazine, but Hisin’s authority broke through this publication, because the review was like this: “in your dark Russia they don’t know how to replicate DNA.” Thank you.

Boris Dolgin: Ideas about the level of scientific research in a particular country in the absence of a rigid clear system of reviewing articles, when they use general ideas, is a problem.

Alexey Bobrovsky: As for the English language, everything is very simple - it is an international scientific language. Any scientist engaged in science, for example, in Germany, a German publishes almost all of his articles in English. By the way, a lot of dissertations are defended in English in Germany, for example, I'm not talking about Denmark, Holland, if only because there are a lot of foreigners there. Science is international. Historically, the language of science is English.

Boris Dolgin: So it happened recently, before the language of science was German.

Alexey Bobrovsky: Relatively recently, but, nevertheless, now it is so, so the transition to English was obvious, at least at the level of abstracts and attestation things, so that normal Western scientists could read these abstracts, give feedback, evaluate, in order to get out of our swamp, Otherwise, it will all completely sink into no one knows where and will remain a complete profanity. It is already happening in many ways now, but we must somehow try to get out of this swamp.

Boris Dolgin: Open the vents so that there is no smell.

Alexey Bobrovsky: At least start to ventilate.

Boris Dolgin: Good. Thank you. This is an optimistic recipe. In fact, your trajectory inspires optimism, despite all the pessimism.

Alexey Bobrovsky: We deviated again from the fact that the main idea of ​​the lecture is to demonstrate to you how beautiful and interesting liquid crystals are. I hope that everything I said will cause some interest. Now you can find a lot of information about liquid crystals, first of all. And secondly, regardless of any conditions, scientists will always exist, nothing can stop scientific progress, this also inspires optimism, and history shows that there are always people who move science forward, for whom science is above all.

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MOSCOW, August 21 - RIA Novosti. Employees of the Faculty of Chemistry and the Faculty of Fundamental Physical and Chemical Engineering of Moscow State University named after M.V. Lomonosov, in collaboration with foreign colleagues, synthesized and investigated new light-sensitive liquid crystal polymers. The work was carried out as part of a project supported by a grant from the Russian Science Foundation, and its results were published in the journal Macromolecular Chemistry and Physics.

Moscow State University scientists in collaboration with Czech colleagues from the Institute of Physics (Prague) have synthesized and studied new LC polymers that combine the optical properties of liquid crystals and the mechanical properties of polymers. Such polymers can quickly change the orientation of molecules under the action of external fields and at the same time are able to form coatings, films, and parts of complex shapes. An important advantage of such systems over low-molecular-weight liquid crystals is that LC polymers at room temperature exist in a glassy state that fixes the orientation of molecules.

© Alexey Boblrovsky, Moscow State University

© Alexey Boblrovsky, Moscow State University

LC polymers are composed of high molecular weight molecules called macromolecules. They have a comb-like structure: light-sensitive "hard" azobenzene fragments (C₆H₅N=NC₆H₅) are attached to the main flexible polymer chain with the help of a "decoupling" of sequentially connected CH2 molecules. These fragments tend to be ordered and can form various types of "packings" - liquid crystal phases. When such polymers are exposed to light, the azobenzene groups rearrange, causing the optical properties of the polymers to change. Such polymers are called photochromic.

Scientists paid special attention to the processes of photoisomerization and photoorientation. Photoisomerization is the rearrangement of bonds within a polymer molecule under the action of light. Photoorientation is a change in the orientation of hard azobenzene (in this case) fragments under the action of linearly polarized light, in the beam of which the direction of electric field oscillations is strictly defined. During the cycles of photoisomerization under the action of polarized light, the azobenzene fragments change their angle. This occurs until the moment when their orientation becomes perpendicular to the plane of polarization of the incident light, and the fragments are no longer able to absorb light.

First, scientists from Moscow State University, in collaboration with colleagues from the Institute of Physics of the Academy of Sciences of the Czech Republic, synthesized monomers, from which LC polymers were obtained at Moscow State University. The phase behavior and temperatures of phase transitions of polymers were studied by the authors using polarization optical microscopy and differential scanning calorimetry. The detailed structure of the phases was studied by X-ray diffraction analysis at the Faculty of Fundamental Physical and Chemical Engineering of Moscow State University.

© Russian Academy of Sciences

© Russian Academy of Sciences

One of the authors of the article, Professor of the Russian Academy of Sciences, Doctor of Chemistry, Chief Researcher of the Department of Macromolecular Compounds, Faculty of Chemistry, Moscow State University named after M.V. Lomonosov Alexey Bobrovsky: "Photoisomerization and photoorientation open up great prospects for creating so-called smart materials. They respond to various external influences and can be used to store, record and transmit information in optical devices of varying complexity. These specific polymers are unlikely to be used in practice "because they are too expensive and their synthesis is not easy. On the other hand, it is far from always possible to predict which systems, when and how they will find application," the scientist concluded.

Liquid crystal polymers (LCPs) are a class of unique thermoplastics that contain primarily benzene rings in polymer chains, which are rod-like structures organized in large parallel matrices. They are highly crystalline, naturally flame retardant, thermotropic (melt oriented) thermoplastics. Although similar to semi-crystalline polymers, LCPs have their own distinct characteristics.

Rice. 1. Typical structureliquid crystal polymer - Ticona.

Traditional semi-crystalline polymers, when melted, have a chaotic (disordered) structure, which, as it cools, forms highly ordered crystalline regions surrounded by an amorphous matrix. The LCP molecules remain well ordered even in the melt, and easily slip past each other when sheared. As a result, they have a very low melt viscosity, which makes it easy to fill very thin walls and reproduce the most intricate shapes. They exhibit very little (or no) shrinkage in the direction of flow and take very little time to set or cure. To keep the process precise, many fabricators and designers are using liquid crystal polymers to make parts with thin walls that may need to withstand high temperatures.

Rice. 2. Viscosity for various polymers, including liquid crystal produced by the companyTicona.

Vectra E130: LCP electric brands
Vectra Liquid Crystalline Polymers (LCP), manufactured by Ticona (the engineering polymers division of Celanese/Hoechst AG), are highly crystalline, thermotropic (melt oriented) thermoplastics that can produce exceptionally precise and stable dimensions, excellent high temperature performance, high rigidity and resistance to chemicals when used to produce very thin walls. The polymer also has a low coefficient of thermal expansion, the same in all three axial dimensions (x,y,z). It withstands surface mount soldering temperatures, including temperatures required for lead-free soldering. Such properties have led to the use of Vectra LCP for many electronic applications such as: sockets, coils, switches, connectors and sensors. Many grades have outperformed ceramics, thermosets, and other high temperature plastics without producing carbon residue (or a negligible amount).
When Vaupell Industrial Plastics needed to create an interior battery case cover for a military precision night vision device, they used the Vectra E130i LCP to ease product development by virtually eliminating mold shrinkage. The product also provided excellent durability over a wide temperature range.

Rice. 3. Battery case for infrared night vision device molded by Vaupell Plastics Industries fromVectra LCP companies Ticona .

The inner gasket of the battery case is inserted into the aluminum outer shell, the gap between them is no more than 0.05mm. The part, made in the form of a clover leaf, has a maximum cross-sectional dimension of 5.08 cm. The length is also 5.08 cm, the walls, open at the bottom and top, have a thickness of 0.56 mm. A rounded flange around the top edge keeps it in position inside the outer shell.

Next generation high strength LCPs
DuPont's next-generation liquid crystal polymer resin performance grades, Zenite LCP, hold promise for greater strength, rigidity, and precision in electronic device connectors and other molded components. Tests have shown that connectors molded from Zenite 6130LX provide excellent resistance to damage during automated pin insertion and board assembly. The new resin can also be used to produce parts with less deformation, which improves part fit and increases the soldering yield point. In destructive testing of the backplane head, the new resin gives a 21% increase in fracture resistance, a 32% increase in deflection before failure, and a more elastic/less brittle fracture pattern. The test uses a press equipped with a tool with a tapered end to push apart the walls of the connectors. The breaking force and deflection of the walls were measured. The improvement in strength and stiffness is also evident compared to standard data for tensile strength, tensile strength, flexural modulus and flexural strength.

Rice. 4.Zenite LCP next generation from DuPont Plastics promise stronger electronic connectors.

Molded connector samples made from Zenite 6130LX also showed a significant improvement in line strength. When the contacts were placed in test specimens made from early generation LCPs, small cracks appeared on the solder lines. No cracks were found on parts molded from the new resins. Other tests have shown that parts made from the new resin are less deformed. The convergence of the side walls of the tested connector was 23% less than the convergence of the part molded from the early generation LCP. Zenite 6130LX is also more resistant to various soldering conditions. Its bending heat resistance is 280ºC, which is 15ºC higher than other LCPs. The most typical applications include a wide range of components for: electrical/electronics industry, lighting, telecommunications, automotive ignition and fuel loading systems, aerospace industry, fiber optics, engine manufacturing, imaging devices, sensors, furnace equipment, fuel structures and gas barriers, etc.

Vectra MT LCP medical grades
Vectra liquid crystal polymer has replaced stainless steel in a wide range of medical applications. Some grades of Vectra LCP comply with USP Class VI regulations and are resistant to gamma radiation, steam autoclave and most chemical sterilization methods.

Rice. 5. Syringe without needle, molded fromVectra LCP MT companies Ticona .

Ticona has eight grades of Vectra LCP MT for use in medical technology (MT) applications such as medical devices, drug packaging and delivery systems, and other healthcare applications. Ticona's MT grades meet USP 23 Class VI requirements for skin, blood and tissue biocompatibility. Ticona's grades for medical applications also comply with the European Community Directive 2002/72/EC for food contact applications and BfR standards respectively. BfR stands for German Federal Institute for Risk Assessment (formerly BgVV, German Federal Institute for Consumer Health and Veterinary Medicine). Ticona Vectra LCP resins for medical technology provide drug and equipment manufacturers with a wide range of design and processing options. This includes filled and unfilled grades for injection molding and extrusion processing, as well as grades with various flow properties and additives, which produce parts with low friction and high wear resistance, improved appearance, higher rigidity and other properties. Vectra LCP MT grades give excellent strength, stiffness, creep resistance, dimensional stability and high flow for long thin sections. They have excellent heat and chemical resistance and are able to withstand repeated sterilization cycles. They can replace metal in medical and dental equipment, be used in highly structured components of drug delivery systems, and meet the needs of devices for minimally invasive surgery and other fields.

1.3.2. Moments of distribution and average molecular weights

1.3.3. Polydispersity parameter

1.4. Stereochemistry of polymers

1.4.1. Chemical isomerism of units

1.4.3. stereoisomerism

Chapter 2. Physics of polymers

2.1. Physics of macromolecules

2.1.1. Perfect tangle

2.1.2. Real chains. Excluded volume effect

2.1.3. Chain Flexibility

2.2. The nature of the elasticity of polymers

2.2.1. Thermodynamic components of the elastic force

2.2.2. Elasticity of an ideal gas

2.2.3. Elasticity of an ideal coil

2.2.4. Elasticity of the polymer mesh

2.3. Viscoelasticity of polymer systems

2.3.1. Maxwell's model. Stress relaxation

2.3.2. Reptation theory

2.3.3. Kelvin model. Creep

2.3.4. Dynamic viscoelasticity

2.3.5. Relaxation properties of polymers. Superposition principle

Chapter 3

3.1. Thermodynamics of polymer solutions

3.1.1. Used thermodynamic concepts and quantities

3.1.2. Principles for calculating the enthalpy and entropy of mixing

3.1.3. Flory-Huggins theory

3.1.4. Colligative properties of polymer solutions. Osmotic pressure

3.1.5. State equation. Thermodynamic characteristic of the solution

3.1.6. Excluded volume and thermodynamic properties of the solution

3.1.7. limited solubility. Fractionation

3.2. Properties of polymer solutions

3.2.1. Swelling. Gels

3.2.2. Viscosity of dilute polymer solutions

3.2.3. Concentrated polymer solutions

3.3. Polyelectrolytes

3.3.1. Effect of Charges on the Conformations of Macromolecules

3.3.2. Interaction of charged chains with counterions. Grid collapse

3.3.3. Properties of polyelectrolyte solutions

3.4. Liquid crystal state of polymers

3.4.1. The nature of the liquid-crystalline state of matter

3.4.2. The influence of temperature and fields on liquid crystal systems

3.4.3. Viscosity of solutions of liquid crystal polymers

3.4.4. High strength and high modulus liquid crystal polymer fibers

Chapter 4

4.1. Crystalline polymers

4.1.1. crystallization conditions. The structure of the polymer crystal

4.1.2. Kinetics of crystallization

4.2. Three physical states of amorphous polymers

4.2.1. Thermomechanical curve

4.2.2. Glassy and highly elastic states of polymers

4.2.3. Viscosity state of polymers

4.2.4. Plasticization of polymers

4.3. Mechanical properties of polymers

4.3.1. Deformation properties of polymers. Orientation

4.3.2. Theoretical and real strength and elasticity of crystalline and amorphous polymers

4.3.3. Mechanics and mechanism of failure of polymers

4.3.4. Impact strength of polymers

4.3.5. Durability. Fatigue strength of polymers

4.4. Electrical properties of polymers

4.4.1. Polymer dielectrics

4.4.2. Relaxation transitions

4.4.3. Synthetic metals

Chapter 5

5.1. Radical polymerization

5.1.1. Initiation of radical polymerization

End of table 5.1

5.1.2. Elementary reactions and polymerization kinetics

1. Initiation.

2. Chain growth.

3. Open circuit.

5.1.3. Molecular weight distribution during radical polymerization

5.1.4. Effect of Temperature and Pressure on Radical Polymerization

5.1.5. Diffusion model of chain termination. Gel effect

5.1.6. catalytic transmission chain

5.1.7. Pseudo-living radical polymerization

5.1.8. emulsion polymerization

5.2. Cationic polymerization

5.2.1. elemental reactions. Kinetics

5.2.2. Pseudo-cationic and pseudo-living cationic polymerizations

5.2.3. Effect of solvent and temperature

5.3. Anionic polymerization

5.3.1. Basic initiation reactions

5.3.2. Kinetics of anionic chain termination polymerization

5.3.3. living polymerization. Block copolymers

5.3.4. Group transfer polymerization

5.3.5. Influence of temperature, solvent and counterion

5.4. Ion-coordination polymerization

5.4.1. Ziegler-Natta catalysts. Historical aspect

5.4.2. Polymerization on heterogeneous Ziegler-Natta catalysts

5.4.3. Anion-coordination polymerization of dienes

5.5. Synthesis of heterochain polymers by ionic polymerization

5.5.1. Carbonyl compounds

5.5.2. Ring-opening polymerization of esters and epoxides

5.5.3. Polymerization of lactams and lactones

5.5.4. Other heterocycles

5.6. Step polymerization

5.6.1. Equilibrium and non-equilibrium polycondensation

5.6.2. Kinetics of polycondensation

5.6.3. Molecular weight distribution of the polymer during polycondensation

5.6.4. Branched and cross-linked polymers

5.6.5. Phenoplasts, aminoplasts

5.6.7. Polyurethanes. Polysiloxanes

5.6.8. Rigid-chain aromatic polymers

5.6.9. Hyperbranched polymers

5.7. General issues of polymer synthesis

5.7.1. Thermodynamics of synthesis

5.7.2. Comparison of ionic and radical polymerization

5.7.3. On the Generality of Pseudo-Living Polymerization Processes

Chapter 6

6.1. Quantitative theory of copolymerization

6.1.1. Copolymer Composition Curves and Relative Activities of Monomers

6.1.2. Composition and microstructure of the copolymer. Statistical approach

6.1.3. Multicomponent copolymerization

6.1.4. Copolymerization to deep conversions

6.2. Radical copolymerization

6.2.1. Copolymerization rate

6.2.2. The nature of the preterminal link effect

6.2.3. Effect of Temperature and Pressure on Radical Copolymerization

6.2.4. Alternating copolymerization

6.2.5. Influence of the reaction medium

6.2.6. Relation between the structure of the monomer and the radical and the reactivity. q-e scheme

6.3. Ionic copolymerization

6.3.1. Ka I ionic copolymerization

6.3.2. Anionic copolymerization

6.3.3. Copolymerization on Ziegler-Natta catalysts

Chapter 7

7.1. Characteristic features of macromolecules as reagents

7.1.1. Influence of neighboring links

7.1.2. Macromolecular and supramolecular effects

7.2. Crosslinking of polymers

7.2.1. Drying paints

7.2.2. Rubber vulcanization

7.2.3. Epoxy curing

7.3. Destruction of polymers

7.3.1. Thermal destruction. Cyclization

7.3.2. Thermal oxidative degradation. Combustion

7.3.3. Photodestruction. Photooxidation

7.4. Polymer-analogous transformations

7.4.1. polyvinyl alcohol

7.4.2. Chemical transformations of cellulose

7.4.3. Structural modification of cellulose

Literature

3.4. Liquid crystal state of polymers

3.4.1. The nature of the liquid-crystalline state of matter

The structure of substances in the liquid crystal state is intermediate between the structure of a liquid and a crystal. This intermediate state is called mesomeric, from "mesos" - intermediate. There are several types of mesophases:

liquid crystals, which can be called positionally disordered crystals or orientationally ordered liquids, they are formed by anisotropic (elongated) molecules, including rigid-chain macromolecules;

plastic crystals formed by molecules with a small shape anisotropy, polymer globules, they are characterized by the presence of a positional order and the absence of an orientational order;

condis-crystals formed by flexible chain macromolecules and organic cyclic structures.

Molecules or fragments of macromolecules that form mesophases are called mesogenic, and the corresponding crystals are called mesomorphic. The most common property of liquid crystals is the anisotropy of properties, which leads, in particular, to their turbidity. It is thanks to this feature that liquid crystals were discovered at the end of the 19th century. F. Reinitzer - when the temperature was lowered, the liquid substance cholesteryl benzoate became cloudy and then became transparent when it was raised. The existence of a clearing temperature is one of the characteristic features of the presence of liquid crystal ordering. Another characteristic sign of mesophase formation is a slight thermal effect. The type of molecular packing, its characteristic pattern - "texture", are determined in a polarizing microscope. The parameters of the liquid crystal structure are determined by X-ray diffraction analysis. Liquid crystals formed in melts during the melting of crystalline bodies are called thermotropic. Liquid crystals that appear in solutions when their concentration changes are called lyotropic.

The first scientists who predicted the possibility of mesophase formation by polymers were V.A. Kargin and P. Flori. In the 1960s liquid-crystal ordering was discovered first for rigid-chain, then for flexible-chain polymers. An important advantage of liquid crystal polymers over low molecular weight liquid ones is the ability of the former to vitrification, due to which the liquid crystal structure is fixed in the solid state. This circumstance significantly expands the areas of practical use of the phenomenon under consideration, in particular, in devices for recording and storing information.

The main criterion for the possibility of polymer transition to the mesomorphic state is the ratio of the length of a substituent segment or fragment to the diameter x = L/d >> 1, which is satisfied by aromatic polyamides, cellulose ethers, -helical polypeptides, DNA, comb-like polymers, etc. The given characteristic ratio allows one to calculate phase transition concentration:

where A is a constant equal to 5-10. This relation holds well for lyotropic systems, i.e. solutions of rigid-chain polymers with various flexibility mechanisms - persistent, rotational isomeric, freely articulated. There are three main types of crystalline phase: nematic, smectic and cholesteric (Fig. 3.16). In the first, the molecules tend to orient themselves along one preferred direction; in the second, along the predominant direction, represented by a spiral; in the third, along with the orientation of molecules, there is a long-range translational order in one or more dimensions, in other words, layered order.

The liquid-crystal phase can form in solutions and melts of rigid-chain polymers, as well as copolymers whose macromolecules contain flexible and rigid sections. The liquid-crystalline ordering of polyphosphazene, polydiethylsiloxane, and polydipropylsiloxane polymers, which obviously do not meet the L >> d criterion, suggested that, under certain conditions, chain hardening, spontaneous straightening, and subsequent packing into the so-called condis-crystal is possible. This term refers to a conformationally disordered crystal with elongated chains.

The first theory of liquid-crystal nematic ordering of a polymer was proposed by L. Onsager in 1949 for a model solution of long cylindrical rods of length L and diameter d under the condition L >> d. If a solution of volume V contains N rods, then their concentration c and volume fraction φ are respectively equal:

Due to the thermal motion of macromolecules, the orientation of their long axes along one direction with liquid crystal ordering cannot be strict, their distribution in directions relative to a given one is characterized by the distribution function . For the system under consideration, the product is equal to the number of rods per unit volume with directions lying inside a small solid angle. around the vector . The vector can take any direction, while for an isotropic solution = const, for an ordered solution it has a maximum at a direction coinciding with the direction of orientation.

In Onsager's theory, the Gibbs function of the solution of rods is expressed as the sum of three terms:

where G 1 represents the contribution to the Gibbs function associated with the movement of the rods, G 2 takes into account the entropy losses that are inevitable during the transition to an ordered state. Of greatest interest is the third term G 3 related to the Gibbs function (free energy) of the interaction of the rods. According to Onsager,

where B(γ) is the second virial coefficient of interaction of the rods, the long axes of which make an angle y between themselves. In this case, the interaction of the rods is limited only by their possible repulsion due to mutual impermeability. Therefore, the value of B(γ) is equal to the volume excluded by one rod for the movement of another.

From Figure 3.17 it follows that the excluded volume and, therefore, B(γ) are equal to:

which corresponds to the parallelepiped shown in Fig. 3.17.

It can be seen from (3.118) that for γ → 0, G 3 → 0, hence, the orientational ordering or, in other words, the arrangement of rods parallel to each other is thermodynamically advantageous, since it leads to a decrease in the Gibbs function of the system. This conclusion is of a general nature. The type of molecular packing of the mesophase, its texture, no matter how bizarre it may be, always corresponds to the minimum value of the Gibbs function.

In Onsager's theory, the following final results are obtained.

1. Orientational ordering in a solution of long rigid rods is a second-order phase transition.

2. For φ< φ i , раствор изотропен, при φ >φ a - anisotropic, at φ i< φ < φ a раствор разделяется на две фазы - изотропную и анизотропную.

3. The transition regions are associated with the characteristics of the asymmetry of the macromolecule:

Liquid-crystal ordering in a solution of rigid rods was also theoretically studied by Flory on the basis of the lattice model of the solution. He derived the following relationship relating the critical concentration and the asymmetry parameter:

Upon reaching the concentration of rods or rod-like rigid-chain macromolecules equal to , the solution is divided into two phases - isotropic and anisotropic (liquid-crystal). With an increase in φ 2 >the relative amount of the first decreases, the second - increases, in the limit, the entire solution will become liquid-ordered. The general view of the phase diagram of a solution with liquid-crystal ordering of rod-shaped molecules was obtained for the first time by Flory. It corresponds to the one shown in Fig. 3.18 phase diagram of a synthetic poly-γ-benzyl-L-glutamate polypeptide solution. The upper left part of the diagram corresponds to the isotropic phase, the upper right part corresponds to the anisotropic phase, the middle part bounded by the curves corresponds to the coexistence of the isotropic and anisotropic phases.

Diagrams of this kind are characterized by the existence of a narrow phase separation corridor. It is believed that it should converge at a point corresponding to the hypothetical transition temperature of the polymer from the isotropic to the liquid crystal state. It is clear that this point should be located in the upper right corner of the diagram, hence it follows that as the temperature rises, the corridor should narrow and turn to the right. When the temperature rises above 15°C (beginning of the corridor), the ratio of polymer concentrations in the coexisting isotropic and anisotropic phases differs relatively little - (Ф 2) from /(Ф2) anis = 1.5. This result was predicted by Flory. At T< 15 °С в широкой двухфазной области концентрация полимера в анизотропной фазе (φ 2 ≈ 0,7 - 0,85) значительно выше по сравнению с изотропной (φ 2 ≈ 0,01-0,05).

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